Nerve And/Or Muscle Stimulation Electrodes

ABSTRACT

A nerve or muscle stimulation apparatus including a nerve stimulation array electrode including a substrate for application to the skin of a user bearing an array of electrodes arranged to be brought into electrical contact with the skin of a user when the substrate is positioned on the skin; one or more input contacts, the or each input contact being switchably electrically connected to a group of electrodes including some or all of the electrodes; and a user operable switch for performing the electrical connection between the or each input contact and any selected one or ones of its respective group of the electrodes.

The present invention relates to the biomedical arts, particularlyneuromuscular electrical stimulation (NMES) by means of surfaceelectrodes and includes apparatus for interfacing an electronicstimulator and a surface electrode with multiple contacts. The inventionfacilitates the selection of the most appropriate positions ofelectrodes used for stimulation of sensory-motor systems in humans.

Electrical stimulation of nerves and muscles by means of surfaceelectrodes is now being used for various applications, including painreduction, muscle strengthening, activation of paralysed muscles, spinalcord stimulation and training of sensory-motor mechanisms. Common to alluses of surface electrodes for stimulation is that it requires a greatdeal of skill and patience of the user and/or the therapist to place theelectrodes in the optimal position for the function to be performed. Itis impossible to know precisely the pathways of the electrical chargethat should be delivered to sensory-motor systems under the skin. It istherefore difficult to predict precisely which anatomic structures willbe activated for any given position and electrode configuration. Veryoften self-adhering electrodes are used, which must be taken offcompletely before they can be repositioned at a different location onthe skin. This process is not only frustrating and time-consuming, butcan also be painful and compromises the adhesion of the electrode to theskin, leading to an increased consumption of electrodes. Further, it isdifficult to try many different electrode sizes, even if this may havean important effect on the function and subjective perception of thestimulation. For these reasons a non-optimal electrode position andelectrode size are often chosen.

The present invention addresses this problem of the effective use ofsurface electrodes. It is proposed to use a multiple contact surfacestimulation electrode combined with an easy-to-use interface, whichallows the user to rapidly emulate many different electrode sizes andpositions, without actually removing the electrode from the skin duringthe process.

U.S. Pat. No. 6,564,079 discloses an electrode array comprising a commonadhesive substrate carrying a number of spaced electrodes for use inmapping nerve locations. The electrode array is to be connected to aperipheral nerve detection instrument, the nature of which is notdescribed. Contacts lead from each electrode to electronic circuitrycomprising multiplexers and a shift register, but again the exactpurpose of this circuitry is not described. It is not disclosed thatnerves or muscles should be stimulated or that any voltage is to beapplied to the electrodes.

The present invention now provides a nerve or muscle stimulationapparatus comprising:

-   a nerve stimulation array electrode comprising a substrate for    application to the skin of a user bearing an array of electrodes    arranged to be brought into electrical contact with the skin of a    user when the substrate is positioned on said skin,-   one or more input contacts, the or each said input contact being    switchably electrically connected to a group of electrodes    consisting of some or all of said electrodes, and-   user operable switch means for performing said electrical connection    by making and breaking electrical connection between the or each    said input contact and any selected one or ones of its respective    group of said electrodes.

Thus, the array of electrodes provided by the invention allows the arrayto be positioned generally in an area in which precise stimulation ofunderlying nerves or muscles is required and for the array to beconfigured in situ by the selection of an appropriate electrode, orappropriate electrodes as a group or a number of groups, which areideally placed to achieve the desired effects. There is therefore noneed to establish the precise position at which electrical stimulationis required before the electrode is placed or to remove and replace theelectrode to achieve the desired position. Instead, the array may beplaced in approximately the required position and then configured asdescribed above. One therefore avoids the need for extensive trial anderror positioning of electrodes. One is therefore able to select one ormore ideally placed contacts as an interface for the delivery ofcontrolled amounts of electrical charge to sensory-motor systems.

The electrodes may be arranged on the substrate in a random manner or inany desired pattern, but it will generally be convenient if saidsubstrate bears an array of electrodes arranged in rows and/or columns.This includes arrangements in which not every point in a row and columnarray is filled, e.g. hexagonal arrays.

Preferably, there are at least 12 electrodes in the array, more suitablyat least 18 or at least 24 electrodes in the array. However, there maybe fewer electrodes than this, e.g. 6 or more. The fewer electrodesthere are, the more accurate will need to be the placement of the array.

Normally it will be preferable that the electrodes are evenly spreadover the substrate. This will maximise the chance that one or several ofthe electrodes are in the ideal position.

Preferably, the maximum space between adjacent electrodes is no morethan 5 cm. More preferably, it is less, e.g. no more than 2 cm. However,the spacing is preferably substantially less, e.g. no more than 1 cm.Still more preferably, the spacing does not exceed 3 mm. Suitably, thespacing is about 1 mm or does not exceed 1 mm.

Preferably, each electrode is not more that 5 cm in maximum dimension,more preferably no more than 2 cm, e.g. about 1 cm.

The size and spacing of the electrodes is suitably chosen to ensure thatthe charge delivered and the current density will be within safetymargins and standards taking into account the stimulation pattern.Relevant parameters to take into account will include the pulse durationand pulse amplitude.

The switch means may be carried by the substrate. Alternatively, theswitch means may be carried by a separate controller. Suitably, theswitch means comprises a respective manually operable switch associatedwith each electrode.

Optionally, the switch means comprises:

-   an electronic user interface unit adapted to receive a user input    representing an electrode selection and to communicate data signals    representing said selection to an electronic switching unit; and-   a said electronic switching unit adapted to receive said data    signals and to perform connection of selected electrodes to said    input contact(s).

Said electronic user interface unit may be adapted to accept programmingto alter said selection of electrodes to accommodate said selection toalterations in the desired site of stimulation with time or user musclemovement. The desired surface position of stimulation may alter as thepatient's limb moves or as the relevant muscles move under the skinsurface upon stimulation. It should be appreciated also that one of theproblems experienced in this field is that repeated use of nerve ormuscle stimulation apparatus is that by exercising muscles or musclegroups the geometry of the relevant body part is changed, so thatpreviously ideal electrode sites become less than ideal. The arrayelectrode of the invention allows for these changes to be accommodatedeither by responding to the changes with reconfiguration of theelectrode array in a trial and error manner from time to time or by apre-programmed reconfiguration.

Optionally, said electronic switching unit is mounted to said substrateand said electronic user interface unit is remote from said substrateand is wirelessly connected or in wired connection with said electronicswitching unit.

In addition to said array electrode, the apparatus may comprise one ormore further electrodes connected to said switch means. In particular,there may be a common ground or counter electrode, which will notgenerally need also to be in the form of an array, but may be ifdesired.

Preferably, the user operable switch means is operable to makeconnection between the or a said input contact and a first electrode setconstituted by a selected one or selected ones of its respective groupof electrodes and with a second electrode set constituted by a selectedone or selected ones of its respective group of electrodes, leavingdisconnected at least one further electrode positioned between saidfirst and second electrode sets. For instance, it has been noticed thatthe pattern chosen for stimulation of finger extensors is not a simplegeometric shape. It may consist of two separate groups of activeelectrodes, such that one activates two separate muscles that bothstretch the fingers whilst not activating the muscle in between, whichextends the wrist. For situations like this, control arrangements thatallow discontinuously arranged electrodes to be grouped for simultaneousactivation, such as individual on/off switches for each electrode, maybe preferred over arrangements that only allow adjacent electrodes to begrouped.

The apparatus may further comprise a source of nerve or musclestimulation signals connected to the or a said input contact.

The invention will be further described and illustrated with referencebeing made to the accompanying drawings in which:

FIG. 1 is an organisational schematic of apparatus for use in theinvention;

FIG. 2 is a schematic electrical circuit of an array electrodeincorporating switches for use in a first embodiment of the invention;

FIG. 3 illustrates a second embodiment of the invention and shows anarray electrode in plan view and a control unit also in plan view;

FIG. 4 illustrates a third embodiment of the invention, showing theoperational interaction between its components, including a plan view ofits array electrode; and

FIG. 5 shows a fourth embodiment according to the invention and shows anarray electrode in plan view and a control unit also in plan view.

The apparatus of FIG. 1 consists of a controller 1 comprising aninterface for the operator to control the apparatus, a switching means 2which directs the output from a source of electrical stimulation signalsor stimulator 3 to a surface array electrode 4 having multipleelectrodes 5 forming an array and in galvanic contact with the skin. Thearray electrode is shown as rectangular, but may have any shape, e.g. beshaped to fit a specific body-part. The stimulator 3 can be anycommercial or custom-made stimulator suitable for the particularapplication. The switch means 2 directs the output from the stimulator 3to one or more of the multiple electrodes of the array electrode asdetermined by the controller 1. The controller allows sizing, shapingand locating of the active area 6 by the operator before or even duringthe operation.

The controller 1 allows selection of the most appropriate contact pointsfor conducting the electrical signals from the stimulator 3 to thetissue. As illustrated below the interface represented by the controller1 may be mechanical or electronic. Where it is electronic, it maycomprise firmware and software to allow wireless communication of thecontroller 1 and a PC, Lap-top, or handheld computer for computerizedsetup.

Four embodiments of the invention are illustrated in FIGS. 2 to 5. Oneis an integrated user interface, controller and electrode shown in FIG.2; in another the controller and user interface are separate from theelectrode (FIG. 3); in that of FIG. 4, the controller and user interfaceis provided by means of a personal computer; and in the last, eachelectrode is controlled by a respective switch located on a remotelyconnected control box (FIG. 5).

A first embodiment is illustrated in FIG. 2. It consists of an arrayelectrode having a substrate pad searing many electrodes 103. Thesubstrate is adhesive on one face (front) on which are positioned theelectrodes 103 and has miniature tactile switches 102 for manualoperation embedded on the back of the array electrode, opposite thestimulating surface. Each switch connects or disconnects thecorresponding electrode 103 in the array on the other side to/from acommon electrical contact input 101. The switches 102 are designed sothat the on/off state of each switch can be clearly seen by the user. Inuse the electrode is placed roughly over the right location on the skin,whereafter fine-tuning of the placement is done by activating theswitches. The electrode is connected via contact 101 to a single channelof an electronic stimulator as would be any other stimulation electrode.The second electrode (counter electrode) in the circuit could be asingle contact anode, or a similar array electrode.

After the electrode is adhered to the skin, by applying electricalstimulation to contact 101 and closing and opening switches 102, apractitioner or patient can find which electrodes in the arraycontribute most effectively to producing the desired stimulation effect,for instance to produce contraction of a muscle. These may lie adjacentone another or not. A selected set of electrodes may be of any shape andmay include from one up to any number of the available electrodes andmay form one or several contiguous groupings.

Although the illustrated array electrode has only one input connection101 which is connectable in common with each of the electrodes 103 ofthe array, more than one such contact may be provided and then each maybe connectable only to a particular respective group of the availableelectrodes 103. Such groups will usually be exclusive of one another (sothat no electrode 103 is a member of more than one group) but if morecomplex switching and circuitry is employed may be overlapping (so thatsome but not all of the electrodes 103 fall into more than one group).Where groups overlap, preferably not all of the electrodes each fallinto the same two groups.

In this and other embodiments, the electrode may be secured in placeother than by adhesive, e.g. by a strap.

A second embodiment is illustrated in FIG. 3. A controller 201 isconnected to a head-stage 202, by means of a thin and flexible cable206. The head-stage includes a zero-insertion force multi-connector 203which connects to an array electrode 204. The head-stage also includesan electronic switching circuit, and the number of conductors in thecable 206 can be kept at a minimum (3-4 leads) sufficient to communicateneuromuscular stimulating signals and data defining electrodes of thearray to receive such signals. Each of the electrodes 205 is representedby a light emitting diode 207, or other indicator, on the controller201. An active indicator light shows that the corresponding electrodecontact is connected to the stimulator. An analog or digital joy-stick212 controls the location, size and shape of the emulated electrode,indicated by the dashed lines 208. Whilst a user is pressing the “Size”button 211, the joystick controls the size and shape of the active areaby moving one corner of the area while keeping the diagonal corner fixede.g. in the upper right, as indicated in the figure. When the “Size”button 211 is released, the shape and size of the active area remainsfixed and can then be moved around within the field by moving thejoystick. A stimulator (not shown) is connected to the controller bymeans of a pair of leads 209 and connectors 210. The controller containsbatteries and may be turned on and off by means of a button 213.

The array electrode 204 again has a substrate having one adhesive facecarrying an array of the electrodes 205, which may be larger or smallerin terms of the number of electrodes than the array actually shown. Eachelectrode is provided with an electrical connection to a respectivecontact 220 of the zif connector plug portion, suitably by a conductivemetal track formed on the substrate.

The circuitry in the head stage 202 is adapted to receive stimulationsignals such as shaped biphasic pulses from the stimulator via thecontroller 201 and data signals from the controller 201 indicating towhich electrodes selected from the whole array the signals should beconnected. Based on these data signals, the circuitry of the head stageacts as a solid state switch means for each electrode of the array toconnect the stimulation signals to the selected electrodes in common.

As in FIG. 2, the electrodes of the array electrode may form a singlegroup from which a selection is made for connection to the samestimulation signals or may be divided into discrete or overlappinggroups to receive the same or different stimulation signals.

Instead of the illustrated joystick arrangement, any alternative manualinput method may be used for determining which electrodes in the arrayare to be connected. For instance, hardware switches (as in FIG. 2) maybe provided on the controller 201 in an array mirroring the electrodearray, as shown in more detail in FIG. 5.

The third embodiment includes a computer 301, which can be a standardPC, laptop or handheld. A touchpad, mouse, joystick, touch-sensitivescreen or other standard pointing device serves as the input means forselecting the active area of the electrode. Different areas and shapesof the active area can be selected on the computer screen, which alsoshows the active area or areas during stimulation. The computer controlsthe switching box, either by a wired or a wireless connection (such as astandard infrared (IR) link or a radio link such as used by wirelesskeyboards and mice). Computer control adds the option of providing rapidchanges in “electrode position”, which could be used for e.g.compensating for movement of the activated muscle. This is an oftenencountered problem when using standard surface electrodes. The motorpoint for a relaxed muscle may be different than that for a contractedmuscle. The movement of the motor point can be entered into thecomputer, which can then compensate for this if it is informed of thetiming and intensity of the stimulation. The latter is done by a triggersignal 302 being sent from the stimulator to the computer as shown or byfeedback signal being sent from a movement sensor responding to changesin the muscle. The switch may be incorporated in a head stage connectedto the array electrode as in FIG. 3.

Another embodiment is illustrated in FIG. 5. It consists of an arrayelectrode 256 having a substrate bearing a plurality of electrodes 257.

The substrate is fabricated from a flexible material in order to bemounted on the selected part of the body. The substrate connects via acable 254 to a controller box 251 with a zero insertion forcemulti-connector 255. The controller box comprises a plurality of tactileswitches 253 that are positioned to match geometrically the positions ofthe plurality of electrodes. The tactile switches have respectiveindicators that by lighting show when each is in the on state. Thecontroller box connects to the anode and cathode 252 of the stimulatorthat delivers monophasic, monophasic compensated, or biphasic bursts ofstimulation pulses. The control box comprises a microcomputer that usesswitches as inputs in order to connect the stimulator output to theselected electrodes in the array electrode.

All electrodes (cathodes) 257 stimulate with respect to a common anode258 connected via a line connector 259, which anode may be a standardsurface electrode or a similar array electrode.

In a modification of this embodiment is a device generally as shown inthe FIG. 5 but where each switch in the array of mechanical switchesshows its state by the position it is in. The controller in such adevice does not require any power and can be made very cheaply.

All embodiments have been illustrated as for a single channel stimulatorto be connected to the device. It is however simple to envision how thedevices can be connected to a multi-channel stimulator. An extrabutton/dial on the user interface can allow the user to setup differentelectrode contact areas for different channels and the controller mustthen be able to differentiate between stimulation pulses entering ondifferent input channels and direct them to the desired electrodecontacts. The channels may be multiplexed, so that no two channels areactive to send out current at precisely the same time.

An example of an application for such a multi-channel device could be astimulation system for restoring hand function. To obtain even arudimentary grasp function of a paralysed hand, it is necessary to applyfour channels of stimulation (finger extension, finger flexion, thumbextension and thumb flexion). Some of (potentially all four) electrodesand the reference electrode in such a system can be replaced by a singlelarge multi-channel electrode of the type described above.

In this specification, unless expressly otherwise indicated, the word‘or’ is used in the sense of an operator that returns a true value wheneither or both of the stated conditions is met, as opposed to theoperator ‘exclusive or’ which requires that only one of the conditionsis met. The word ‘comprising’ is used in the sense of ‘including’ ratherthan in to mean ‘consisting of’.

1. A nerve or muscle stimulation apparatus comprising: a nervestimulation array electrode comprising a substrate for application tothe skin of a user bearing an array of electrodes arranged to be broughtinto electrical contact with the skin of a user when the substrate ispositioned on said skin, one or more input contacts, the or each saidinput contact being switchably electrically connected to a group ofelectrodes consisting of some or all of said electrodes, and useroperable switch means for performing said electrical connection bymaking and breaking electrical connection between the or each said inputcontact and any selected one or ones of its respective group of saidelectrodes.
 2. Apparatus as claimed in claim 1, wherein said substratebears an array of electrodes arranged in rows and columns.
 3. Apparatusas claimed in claim 1, wherein there are at least 12 electrodes in thearray.
 4. Apparatus as claimed in claim 1, wherein there are at least 24electrodes in the array.
 5. Apparatus as claimed in claim 1, wherein theelectrodes are evenly spread over the substrate.
 6. Apparatus as claimedin claim 1, wherein the maximum space between adjacent electrodes is nomore than 5 mm.
 7. Apparatus as claimed in claim 6, wherein the maximumspace between adjacent electrodes is no more than 2 mm.
 8. Apparatus asclaimed in claim 1, wherein the switch means is carried by thesubstrate.
 9. Apparatus as claimed in claim 1, wherein the switch meanscomprises a respective manually operable switch associated with eachelectrode.
 10. Apparatus as claimed in claim 1, wherein the switch meanscomprises: an electronic user interface unit adapted to receive a userinput representing an electrode selection and to communicate datasignals representing said selection to an electronic switching unit; anda said electronic switching unit adapted to receive said data signalsand to perform connection of selected electrodes to said inputcontact(s).
 11. Apparatus as claimed in claim 10, wherein saidelectronic user interface unit is adapted to accept programming to altersaid selection of electrodes to accommodate said selection toalterations in the desired site of stimulation with time or user musclemovement.
 12. Apparatus as claimed in claim 10, wherein said electronicswitching unit is mounted to said substrate and wherein said electronicuser interface unit is remote from said substrate and is wirelesslyconnected or in wired connection with said electronic switching unit.13. Apparatus as claimed in claim 1, comprising in addition to saidarray electrode, one or more further electrodes connected to said switchmeans.
 14. Apparatus as claimed in claim 1, wherein the user operableswitch means is operable to make connection between the or a said inputcontact and a first electrode set constituted by a selected one orselected ones of its respective group of electrodes and with a secondelectrode set constituted by a selected one or selected ones of itsrespective group of electrodes, leaving disconnected at least onefurther electrode positioned between said first and second electrodesets.
 15. Apparatus as claimed claim 1, further comprising a source ofnerve or muscle stimulation signals connected to the or a said inputcontact.